This invention relates in general to apparatus for pumping a liquid, and relates in particular to apparatus for metering a predetermined quantity of a first liquid for mixture with a second liquid.
There are many applications where it is necessary to meter and intermix two liquids or other fluids in some certain predetermined proportion. In the handling and dispensing of beverages, for example, a predetermined quantity of one ingredient such as a beverage concentrate must be intermixed with another ingredient to provide a beverage suitable for consumption. The proportion of concentrate mixed with the carrier or other liquid is usually a fixed proportion in order to maintain the desired taste and other characteristics of the resulting mixed beverage, and even a relatively small departure from the intended proportion of concentrate may produce a significant and easily-detectable departure from the desired taste or appearance of the mixed beverage. For that reason along with others, the ability to provide a consistent and repeatable proportionate mixture of two liquids is most important in the beverage industry. Numerous other instances of commercial or industrial application for metering apparatus will be apparent to those skilled in the art.
Although various types of pumping or dispensing apparatus have been proposed, the liquid metering apparatus of the prior art has proven less than satisfactory for many applications. A simple syphon metering system, depending on the flow of one liquid to provide a reduced pressure for pumping a quantity of a second liquid, makes metering accuracy dependent on velocity and rate of flow, viscosity of the liquids, and on other variables, and has proven difficult to maintain a desired matering proportion with necessary accuracy. While positive-displacement metering apparatus is not new by itself, such apparatus tends to be relatively complex and/or expensive to construct and maintain. Furthermore, positive-displacement liquid pumping apparatus of the prior art generally delivers a fixed volume of pumped liquid with each stroke or cycle of a motor or other driving device, and the volume of pumped liquid can be adjusted, if at all, only with some difficulty or expense.